Genetics Essentials

Genetics Essentials

• Streptococcus pneumoniae was used in Griffith's experiment demonstrating genetic transformation.
• T2 bacteriophage infecting Escherichia coli was used in the Hershey-Chase experiment to confirm DNA as the genetic material.
• Progeny of F1 × F1 mating produces a 3:1 phenotypic ratio with dominant-recessive inheritance.
• ABO blood group is determined by the presence or absence of A and B antigens (O lacks both), inherited via multiple alleles.
• DNA replicates via the semiconservative model; each strand acts as a template.
• Helicase unwinds the DNA helix by breaking hydrogen bonds during replication.
• DNA replication occurs in the S (Synthesis) phase of the cell cycle.
• Okazaki Fragments are short DNA sequences synthesized on the lagging strand during replication.
• Also called a replicon, a Replication Unit is a DNA segment replicated from a single origin.
• Rolling Circle Replication is common in plasmids and viruses, and its a mechanism where DNA replicates in a circular fashion.
• Primosome is a protein complex that synthesizes RNA primers for DNA replication.
• Repliosome is a multi-protein complex that carries out DNA replication at the replication fork.

Transcription and Translation

• RNA polymerase synthesizes RNA from a DNA template during transcription.
• In eukaryotes, RNA polymerase II synthesizes mRNA.
• Rho-dependent and Rho-independent terminators stop transcription in bacteria.
• Monocistronic mRNA codes for one protein, whereas polycistronic mRNA codes for multiple proteins.
• Addition of a poly-A tail to mRNA at the 3’ end is for stability and nuclear export.
• The 5’ cap is a modified guanine nucleotide added to mRNA for stability and ribosome recognition.
• Introns are the non-coding sequences in eukaryotic genes that are removed during splicing to leave exons.
• A codon is three nucleotides long and codes for one amino acid.
• The genetic code is universal, redundant, unambiguous, and read in triplets.
• A DNA sequence 5’-ATGC-3’ transcribes to mRNA 5’-UACG-3’.
• AUG is the start codon, it codes for methionine, and signals the start of translation.
• Bacterial ribosome consists of a 30S (small subunit) and a 50S (large subunit), forming a 70S ribosome.

Mutation and Mutagens

• Germline mutation is a heritable mutation occurring in gametes and can be passed to offspring.
• The Luria-Delbrück experiment, also known as the Fluctuation Test, proved that mutations occur randomly before selection.
• A Point mutation is a single nucleotide change in DNA, including substitutions, insertions, or deletions.
• Transversion mutation is a point mutation where a purine is replaced by a pyrimidine or vice versa.
• Forward mutation changes a wild-type allele into a mutant form.
• Ionizing radiation (X-rays, gamma rays) and non-ionizing radiation (UV rays) are types of radiation.
• Thymine dimers are DNA damage caused by UV radiation, leading to covalently linked adjacent thymines.
• Alleles are different versions of a gene found at the same locus on homologous chromosomes.
• Ethidium bromide, acridine orange, and proflavine are examples of Intercalating Agents that insert into DNA.
• Nitrous acid, hydroxylamine, and alkylating agents are examples of Base-modifying Agents that modify DNA bases.
• Salmonella typhimurium is used in the Ames Test to detect the mutagenic potential of chemicals.
• Auxotrophic mutants are detected by replica plating on selective media to detect nutritional mutants.
• Visible mutants are observed based on phenotypic changes like pigment loss or altered colony morphology.

DNA Repair and Effects of Mutation

• DNA repair includes direct repair, base excision repair, nucleotide excision repair, and mismatch repair.
• A pleiotropic mutation is a single mutation that affects multiple traits in an organism.